BGE: How can I make a hostile animal artificial intelligence?
You need to use states. Basically this will be :

Near property Player > And > State set state 2

It will look like this.



Now on state two, you need an Always sensor rigged up to a Steering acctuator with the player being the target object.

To avoid being stuck in state 2 forever, make something to switch back when the player isn't nearby anymore.